Diastereoselective Metabolism of a Novel Cis-Nitromethylene Neonicotinoid Paichongding in Aerobic Soils

Abstract

Many pesticides are chiral but used as racemic mixtures, even though their stereoisomers are often degraded stereoselectively in soils. Evaluation of degradation of chiral compounds is mostly focused on the enantioselectivity rather than diastereoselectivity/epimer preferences. In this study, we explored the diastereoselective transformation of paichongding (IPP), a novel chiral neonicotinoid with broad-spectrum insecticidal activity, to several degradation intermediates in different soils. (14)C-Labeling coupled with LC-MS/MS and high resolution MS were used to track residues of IPP and identify major transformation metabolites. The stereoisomers of IPP known as 5R, 7R-IPP (RR-IPP), 5S, 7S-IPP (SS-IPP), 5S, 7R-IPP (SR-IPP), and 5R, 7S-IPP (RS-IPP) showed diastereoselective/epimer-selective persistence in all soils except an acidic clay soil. Moreover, IPP was transformed to a range of degradation intermediates (M1-M6), which also showed significant diastereoselective and soil preferential formation. Depropylation, nitrosylation, denitration, demethylation, dehydroxylation, and ketonization contributed to IPP transformation. The diastereoselective degradation of the parent compound and formation of incomplete intermediates implies that diastereomers/epimers should be regarded as different chemicals. The approach of coupling (14)C and MS may be used as an effective tool to understand the environmental processes and risks of other man-made chiral compounds.

Stereoselective Degradation and Transformation Products of a Novel Chiral Insecticide, Paichongding, in Flooded Paddy Soil

“…The same amount of nitrogen-purged deionized water was added to compensate for evaporated loss of water. At 0, 5,11,20,31,45,60,76, and 100 days after the treatment, the flow-through vacuum desiccators were flushed for 30 min with a continuous nitrogen stream (99.99% pure). Soils without 14 C-stereoisomers were incubated as controls.…”

“…Interestingly, the activities against alfalfa aphids of the four stereoisomers of paichongding differed significantly, with (5R,7S)-> (5S,7S)-≥ (5S,7R)-> (5R,7R)paichongding. 20 Li et al reported that mineralization, extractable residues, and bound residue formation of paichongding were diastereoselective. 21 Wang et al found that after foliar application, no stereoselective absorption was observed among the enantiomers of paichongding, whereas significant stereoselective translocation in plants was observed between its epimers.…”

Identification of Less Harmful Pesticides against Honey Bees: Shape-Based Similarity Analysis

“…From literature [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], a dataset of 302 compounds with known pesticide activity was selected and used further for a 3D-similarity search. The conformational space of selected compounds was carried out with the Omega tool, Openeye (OMEGA v.2.5.1.4, OpenEye Scientific Software, Santa Fe, NM, USA.…”

Fate Characterization of Benzene Kresoxim‐Methyl (a Strobilurin Fungicide) in Different Aerobic Soils

“…Experiments were conducted using the methods of Fu et al (2013). Before spiking with 14 C‐BKM, the soils were incubated in the dark for 15 d, and their water‐holding capacity was adjusted to 40% using distilled water to revive microbial activity.…”

“…Treated soil samples were transferred to 500‐mL Erlenmeyer flasks that were subsequently attached to a flow‐through apparatus with a series of airtight flasks containing absorbent solutions, as described by Fu et al (2013). The trap solutions were refreshed periodically throughout the incubation period.…”